1. Field of the Invention
The present invention relates to motor control devices for performing synchronous control such that rotational speeds and rotation amounts of a plurality of motors become equal.
2. Description of the Related Art
In a convertible vehicle having a roof that can be freely opened and closed on the upper part of a vehicle compartment, the roof being folded and accommodated in a back trunk, a movable body such as roof and trunk is moved by rotating two motors arranged on the right and the left. However, when the rotational speeds and the rotation amounts (rotation angles) of the two motors differ due to variation in motor properties, variation in friction force of a link mechanism driven by the motors or difference in load of the motors caused by the tilt of the vehicle body, imbalanced force acts on the movable body, whereby the movable body may be deformed, or in an extreme case, broken.
A control device that performs control such that the rotational speeds and the rotation amounts of the two motors become equal is proposed in Japanese Patent No. 3467440, Japanese Patent No. 3550114, and Japanese Patent Application Laid-Open No. 2001-51722. In Japanese Patent No. 3467440, a target position after the lapse of a unit time is calculated from a current position and a target speed of each motor, a predictive position after the lapse of the unit time is calculated from the current position and a current speed of each motor, and the output amount of the motor is determined by comparing the calculated target position and the predictive position, so that control can be performed to have the predictive positions of the respective motors gradually approach a common target position thereby suppressing positional shift between the motors. In Japanese Patent No. 3550114, speed control similar to a conventional technique is performed on a first motor, and position control is performed on a second motor instead of the speed control with an absolute value of the rotation angle of the first motor as a reference so that the second motor synchronizes and follows the absolute value of the first motor thereby suppressing positional shift between the motors. In Japanese Patent Application Laid-Open No. 2001-51722, the two motors are controlled such that the rotational speeds are matched and the operation is stabilized by using means for switching a speed feedback path from an anti-backlash control to speed control according to the rotational speed of the motor.
Since the rotational speeds and the rotation amounts cannot be independently controlled in the conventional motor control device, the rotational speed is influenced when control is performed to eliminate difference in rotation amounts between the two motors, thereby creating a difference in the rotational speeds of the motors. FIG. 3 shows one example of a control result of the rotation amounts of the two motors and tip speed of the movable body driven by the motors. FIG. 3A shows the control result of the rotation amounts of the motors A, B. FIG. 3B shows the control result of the tip speed of the movable body. The tip speed and the target speed are substantially matched, as shown in FIG. 3B, by synchronously controlling the motors A, B so that the rotational speeds become equal. However, in the case where difference is created in the rotation amounts of the motors A, B, as in FIG. 3A, even when synchronous control of the rotational speeds is performed, such difference can be resolved by controlling the rotation amount of each motor so that the difference becomes 0, but change in operation amount of the rotation amount influences the operation amount of the rotational speed, whereby a difference is created in the rotational speeds of the motors A, B and the tip speed deviates from the target speed. Therefore, control to eliminate the difference in rotation amount while maintaining the rotational speeds equal between the motors cannot be carried out in conventional techniques.